Comparative study of polypyrrole films electrosynthesized in alkaline and acid solutions

I.L. LEHR; O.V. QUINZANI; S.B. SAIDMAN

Foz do Iguaçu, Brasil

Congreso; ISE 2008 Spring Meeting; 2008

International Society of Electrochemistry

Stable and electroactive polypyrrole (PPy) films were produced by electropolymerization of polypyrrole in alkaline solutions containing nitrate or chloride. It is well known that PPy films electrosynthesized in acid or neutral media suffers a decrease of electrochemical activity in alkaline solutions [1]. On the contrary, the films formed in alkaline medium can be cycled in acid or in alkaline media without loosing electrochemical activity [2]. Thus, these PPy films  should be suitable materials for the construction of electrodes to be used in alkaline solution, a medium which is preferred for several electrochemical reactions related with environmental protection such as nitrate or oxygen reduction. A deeper understanding of properties of these films should be helpful in improving the performance of the polymers. We present the results of ongoing research to understand the different behaviour of PPy films synthesized in both acid and alkaline media. The polymers were electrodeposited onto vitreous carbon electrodes at 0.9 V vs SCE from 0.1 M HCl and 0.1 M NaCl solutions of pH 12 and 13 containing 0.25 M Py. The electrochemical characterization was performed using cyclic voltammetry and electrochemical impedance spectroscopy. Infrared and Raman spectroscopy were conducted to observe the changes during acid and base treatments as well as during thermal ageing. Treatments include exposition to different media during prolonged period (60 days). The IR and Raman study of PPy samples synthesized in acid and alkaline media indicates only little differences between their molecular structures. The stability in alkaline solution of the film formed in the same medium is maintained even if the polymer is exposed to alternating treatment with base and acid. On the other hand, the study of redox cycling of the polymers in the presence of different mobile anions and impedance data indicate that ions diffuse faster in the film electrosynthesized in acid medium. The obtained results are discussed in terms of differences between polymeric chains organization. A less open structure may be formed as the solution pH increases, which is less accessible for reactants. Then, the formation of covalents bonds between PPy and OH- is hindered. The film synthesized in a basic solution is not damaged even if it is exposed to a strongly alkaline medium for a short time. Moreover the closed polymer structure remains unaltered in a low pH solution.